Rotor disc for a disc brake

ABSTRACT

A rotor disc ( 1 ) for a disc brake and the like comprises a circular substrate ( 2 ) made of a thermally conductive material, and two superposed coating layers ( 3 ) and ( 4 ) disposed on both outer circular faces of the substrate. The outer coating layer ( 3 ) is made from a high thermal conductivity and high wear resistant material such as carbon silicon carbide composite or metallic type material. The inner coating layer ( 4 ), is made from a thermally insulating material such as zirconia or other ceramic material. The dimensions of the substrate and layer and the material from which they are made may be tuned for optimum performance. The inner layer ( 4 ) operates to protect the substrate from the heat and high temperatures generated at the outer surface of the disc ( 1 ) in use.

The present invention relates to a rotor disc, particularly, but notexclusively for a disc brake and the like.

Traditionally, brake discs have been made of cast iron. Cast ironexhibits the necessary thermal and strength characteristics for thispurpose. A disadvantage, however, is its weight. In an average motorvehicle with disc brakes on all four wheels the rotor discs of thebrakes may add 40 kg to the weight of the vehicle. This weight iscarried permanently around with the vehicle, although the brakes may beused relatively infrequently, thus adding to fuel consumption andemissions. Making discs of other lighter materials has been proposed butso far a satisfactory solution has not yet been found. For example,aluminium has been suggested but although its thermal properties aregood they are not as good as those of cast iron. These poorer thermalcharacteristics adversely affect the performance of the material as arotor disc.

According to the present invention there is provided a composite rotordisc comprising a substrate made of a thermally conductive material, afirst coating layer on at least one circular face of the disc, the firstcoating layer being made of a thermally insulating material and a secondcoating layer superposed on the first coating layer, the second coatinglayer being made of a wear resistant, thermally conductive materialwhereby the substrate is protected from heat generated at the circularsurface of the disc.

In a preferred embodiment of the invention, the substrate isadvantageously aluminium or other suitable metal or metallic alloy. Thefirst coating layer may advantageously be Zirconia or other ceramic. Thesecond coating layer may advantageously be a carbon-silicon carbidecomposite or other metallic alloy. The thicknesses of the layers andsubstrate advantageously lie in the following ranges. Layers 0.01 to2.00 mm substrate 5-40 mm

In order that the invention may be more clearly understood embodimentsthereof will now be described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 shows a cross section through a part of a rotor disc according tothe invention,

FIG. 2 shows a front elevational view of the rotor disc of FIG. 1,

FIG. 3 shows a cross-section of a modification of the rotor disc ofFIGS. 1 and 2, and

FIG. 4 shows a cross-section of a further modification of the rotor discof FIGS. 1 and 2.

Referring to FIGS. 1 and 2 the rotor disc is indicated generally by thereference numeral 1 and comprises a circular substrate 2 and twosuperposed coating layers 3 and 4 disposed on both outer circular facesof the substrate. The substrate is vented at 5 so that air may circulatethrough the substrate to cool the substrate. The substrate 2 is madefrom a low density but high thermal conductivity material such asaluminium or other suitable metal or metallic alloy. The outer coatinglayer 3 is made from a high thermal conductivity and high wear resistantmaterial such as a carbon-silicon carbide composite or metallic-typematerial. The inner coating layer 4 is made from a thermally insulatingmaterial such as zirconia or other ceramic material.

In operation under braking conditions heat is generated on both surfacesof the disc due to friction between the brake pad shown diagrammaticallyat 6 and the rotor disc 1 as the disc 1 rotates causing the temperatureof the disc 1 to rise. Heat is lost from the disc 1 by conductionconvection and radiation. Heat lost by conduction is to the surroundingair and through the material of the outer layer 3 to inner layer 4 andthrough that layer to the substrate 2 beneath. Heat lost by convectionis to the surrounding air as the air moves relative to all surface ofthe disc including those opening to the vent 5. Heat lost by radiationis lost from all hot surfaces. An exemplary temperature profile throughthe rotor disc 1 is shown at 7. The temperature is at its maximum onboth outer surfaces of the disc 1 where the heat is generated throughthe friction between the disc brake pad 6 and those surfaces. Heat isconducted relatively easily through the outer layers 3, which are madeof a highly thermally conductive and wear resistant material, to theinner layers 4, and the fall in temperature through those layers iscorrespondingly small. Heat conduction through the inner layers 4, whichis made of a thermally insulating material, is restricted and, ascompared with the outer layer there is a greater fall in temperature.The inner layers 4 therefore operate to protect the substrate from theheat and high temperatures generated at the outer surfaces of the disc1. The temperature at the interface between the substrate 2 and theinner layers 4 is much less than that between the outer and inner layers3 and 4 and it continues to fall across the material of the substrateheat flowing through the substrate being removed at the surfacesadjoining the vent 5 by conduction, convection and radiation.

The thickness of the layers 3 and 4 is advantageously in the range 0.05to 5.00 millimetres, preferably in the range 0.01 to 2.00 millimetresand in this example outer layers 3 are 1.0 millimetres thick and innerlayers 4 are 0.5 millimetres thick. The thickness of the substrate liesin the range 5 to 40 millimetres. By appropriately choosing thedimensions of the layers and substrate and the material from which thelayers and substrate are made the thermal behaviour of the rotor discmay effectively be ‘tuned’ for optimum operational performance.

In a modification, a protective layer may be disposed over the outercylindrical surface and adjacent the vent of the substrate as shown inFIG. 3 to protect the substrate against oxidation in all regions notcoated by layers 3 and 4. In this modification parts equivalent to theparts of the embodiment of FIGS. 1 and 2 bear the same referencenumerals. With the above described arrangements heat maybe conductedaround the outer layer(s) 3 and lost by convention from the surfacethereof. Heat from the outer layer(s) may also be dissipated bycontrolled conduction through the inner layer 4 and through thesubstrate 3 and lost by convention from the surfaces adjacent the vent 5in the substrate.

Although the disc has been described with a vent, the vent may bedispensed with. Such an arrangement is illustrated in FIG. 4. In thisfigure parts equivalent to parts in FIGS. 1 to 3 bear the same referencenumerals.

It will be appreciated that the above embodiment has been described byway of example only and that many variations are possible withoutdeparting from the scope of the invention.

1. A composite rotor disc comprising: a substrate made of a thermallyconductive material; a first coating layer on at least one circular faceof the disc, the first coating layer being made of a thermallyinsulating material; and a second coating layer superposed on the firstcoating layer, the second coating layer being made of a wear resistant,thermally conductive material; whereby the substrate is protected fromheat generated at the circular surface of the disc.
 2. The compositerotor disc of claim 1, wherein the substrate is metal.
 3. The compositerotor disc of claim 1, wherein the metal is aluminum.
 4. The compositerotor disc of claim 1, wherein the substrate is a metallic alloy.
 5. Thecomposite rotor disc of claim 1, wherein the full coating layer is aceramic.
 6. The composite rotor disc of claim 5, wherein the ceramic iszirconia.
 7. The composite rotor disc of claim 1, wherein the secondcoating layer is a metallic alloy.
 8. The composite rotor disc of claim7, wherein the metallic alloy is a carbon-silicon carbide composite. 9.The composite rotor disc of claim 1, wherein the thickness of thesubstrate lies in the range 5 to 40 millimeters.
 10. The composite rotordisc of claim 1, wherein the thickness of the layers lies in the range0.05 to 5.00 millimeters.
 11. The composite rotor disc of claim 1,wherein the thickness of the layers lies in the range 0.01 to 2.00millimeters.
 12. The composite rotor disc of claim 1, wherein the firstcoating layer is 0.5 millimeters thick.
 13. The composite rotor disc ofclaim 1, wherein the second coating layer is 1.00 millimeter thick. 14.The composite rotor disc of claim 1, wherein the substrate is vented.15. The composite rotor disc of claim 1, wherein a protective coating isdisposed over the outer cylindrical surface.